1. Field of the Invention
The present invention relates generally to methods and compositions for recording optical information. More particularly, the present invention relates to recording of optical information by causing and detecting pseudorotation or inversion in specific molecules incorporated within a viscous medium.
2. The Background of the Invention
In view of the constant improvements in the field of computer technology, video recording, and the like, it has become necessary to improve the means by which data can be rapidly and accurately recorded and accessed. Furthermore, the increasing dependence upon computer-generated and recorded information and data has created problems in storing the vast amounts of information and data which are now available.
Currently, storage media typically fall into four general classifications: (1) permanent storage media on which information is recorded and then the medium is rendered incapable of further recording; (2) permanent archival storage media which are similar to permanent storage media except that they have a much longer life; (3) postable storage media on which further information can be recorded after the initial recordation of information; and (4) erasable media. It will be readily appreciated that with the ever-expanding uses for data storage, including the storage of audio visual presentations, the need for new and improved recording methods and media in each of these classifications is increasing.
In the past, magnetic tapes or discs have been the most common storage media for information and data. While magnetic storage media have the advantage of being erasable, they also have the disadvantage of being relatively low in storage density. Thus, a large volume of magnetic tape is required to store a relatively small amount of information.
Accordingly, attention has been directed toward the development of optical recording media, which are capable of recording information at a much higher density. Because most optical recording methods and media are not erasable, however, this type of media has been generally used only for archival storage of records, documents, music, and other types of information.
In general, optical recording methods employ a focused laser which is directed into a medium and which induces a chemical or physical change at the point of contact between the laser beam and the recording medium. This typically forms a permanent "spot" on the medium of about one micron in diameter. In order to "write" information, the information is first converted into a digital format. Utilizing a binary format, for example, the information is converted into one of two possible states, which may be thought of as on-off, black-white, yes-no, or 1 and 0. By coupling electrical impulses having a binary format to a light beam modulator, it is possible to reproduce the information as a set of pulses of the laser which are then directed onto the photosensitive medium, there forming white and dark spots.
In order to "read" the information, the medium is scanned by a focused laser at low power. The pattern of white and dark spots is observed to reconstruct the binary code, which in turn can be readily converted back to its original form. A low power laser may be employed in this process in order to prevent further writing on the medium.
As mentioned above, the primary drawback to virtually all existing systems for optical recording of information is that they are not erasable. These systems essentially record information by "burning" spots at specific locations in the subject medium. In order to attempt to overcome this limitation with existing permanent storage systems, it has been thought that certain reversible physical phenomena could be potentially useful in recording information or in inducing certain optical changes in material in response to a certain set of conditions. Photochromism and phosphorescence provide examples of such reversible phenomena.
The phenomenon of photochromism has long been observed in the chemical arts. Photochromism generally relates to the conversion of a material from a colored chemical to a non-colored chemical, or vice versa. Photochromism may also involve conversion of a material from one colored species to a species which produces a different color or color intensity. Photochromism is generally caused by a light induced chemical reaction which converts the photochromic chemical from a molecule having one type of color characteristics to a molecule which has a different set of color characteristics.
Phosphorescence is a somewhat related phenomenon which results from changing the molecule from a rest or ground state to a phosphorescent excited state, generally by bombarding the molecule with light energy. The molecule will eventually reach a metastable triplet state. In the excited phosphorescent state the molecule has different color characteristics than it does in the ground state. It is expected, however, that the molecule will lose the energy provided by the light bombardment and eventually return to its original low energy ground state. That is, the molecule degrades (or phosphoresces) from the high energy "metastable" state, back to the original energy state.
Many uses of phosphorescent and photochromic molecules have been found in the art. For example, photochromic molecules have been incorporated into eyeglasses which change from one color to another color depending on the brightness of the light to which they are exposed. Thus, the glass may darken as the intensity of sunlight increases. Similarly, it has been suggested that such photochromic molecules could be incorporated into automobile windshields in order to darken the windshield when it is exposed to extremely bright sunlight. This type of molecule has also been incorporated into novelty items such as toys and various of types of jewelry.
Photochromic and phosphorescent molecules have also been used in computer and other similar types of electronic equipment. For example, this type of molecule has been used to provide a visual display of data. It has also been suggested that photochromic or phosphorescent molecules could possibly be used in the recording of information in various sorts of memory devices. One type of memory device would be an optical analog computer in which the particular photochromic or phosphorescent state represents the information stored.
As mentioned above, the color changes known in the art are generally either caused by producing an excited state within the molecule by bombarding the molecule with light energy, or from an actual chemical reaction which is initiated or driven by light. In both cases, the change which occurs to the molecule will generally be reversible, at least over the useful life of the molecule.
In order to make photochromic molecules more acceptable for particular uses, particularly if they are to have potential for use in recording information, it is necessary to add them to desirable environments. For example, photochromic molecules have been modified so that they are water soluble and thus can exist in an aqueous environment. In addition, in order to stabilize photochromic compounds, it is sometimes necessary to incorporate them into a crystal lattice or a clay material. Thus, the photochromic molecule may be stabilized at a desired energy state. Other elaborate techniques have also been developed in order to maintain the photochromic molecule in the desired state.
Many of the systems described above, however, effectively render the molecule useless for incorporation into a system for optically recording of information. For example, it is difficult to incorporate a clay or crystal lattice into an information storage system or optical computer. Thus, while these molecules have shown some promise in information storage, practicalities in their handling have prevented the development of actual usable systems.
It will be appreciated that if such handling problems could be overcome, photochromic molecules could clearly be used for the storage of information. As indicated above, when a molecule changes from one state to another state, which states can be easily detected through changes in optical characteristics, it may be possible to record information using this mechanism.
One additional reason that existing systems are not acceptable for data storage, however, is that it is often difficult to maintain the photochromic or phosphorescent molecule in the desired state. This is particularly true when dealing with excited phosphorescent molecules. As mentioned above, photochromic molecules often require stabilization, such as incorporation into some type of mineral lattice, in order to maintain a particular colored state.
Another problem is that photochromic molecules must be chemically converted, through an optically driven chemical reaction, in order to move from one colored state to another. After repeated conversions fatigue often sets in. That is, a molecule can be changed from one molecule to a different molecule only a limited number of times. This fatigue phenomenon is usually due to undesired side reactions which occur within the system. Eventually, the system fails to convert the chemicals as desired and the system must be replaced.
A further problem in the existing art is that large quantities of light are required in order to make the required conversion, thus limiting the use of such systems for recording information. It is not generally practical to provide the large quantities of energy necessary to convert existing photochromic species repeatedly from one state to another within an information storage system. In particular, it would be impossible to use existing systems in a computing device because of the large quantities of light which would be required.
Another limitation in the art is that it is necessary to make fine measurements of color intensity within the photochromic molecule in order to determine what state exists. Because there may exist a color gradient within the subject medium it is sometimes difficult to determine whether the majority of the photochromic molecules are in one state or another. This limitation makes it difficult to accurately record optical information.
It is apparent that what is currently needed in the art is a system for accurately recording optical information which overcomes the problems discussed above. In particular, it would be a significant advancement in the art to provide compositions and methods for recording optical information which could be incorporated into easily handled systems and which do not require a net chemical transformation of the light absorbing chromophore within the optical recording medium in order to operate. It would be a related advancement in the art to provide such methods and compositions which could be incorporated into an easily handled polymeric medium. It would be a further advancement in the art to provide such compositions and methods which required very low light intensity to record and read optical information. It would be another advancement in the art to provide such methods and compositions which could repeatedly save and erase optical information without producing fatigue within the system. It would also be an advancement in the art to provide such a system having a high signal to noise ratio.
Such methods and compositions are disclosed and claimed herein.